If you're both over 65 you don't have to file if your gross income excluding Social Security is less than $21,800. That's the 2012 number; it goes up each year.

You made me curious, especially on behalf of my Mom, and the figure for singles is $11,200 for 2012 (so she doesn't qualify). How do you define "over 65"...if you both turn 65 in 2012, does this rule apply to filing 2012 taxes, or would you need to turn 65 before 2012?

Also...I thought you had to pay income taxes if your income as a couple was at least $32k and $25k for individuals, including Social Security. At least that's what it says on the SSA site:

"You will have to pay federal taxes on your Social Security benefits if you file a federal tax return as an individual and your total income is more than $25,000. If you file a joint return, you will have to pay taxes if you and your spouse have a total income of more than $32,000."

When your statement and SSA's are in conflict, which takes precedence? Do they both need to be true to avoid federal income tax? For example, suppose a 65+ couple gets $40k in SS income and $20k in other income--do they file/pay federal income tax or not?